001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018package org.apache.commons.math4.legacy.ode.nonstiff; 019 020 021/** 022 * This class implements the 3/8 fourth order Runge-Kutta 023 * integrator for Ordinary Differential Equations. 024 * 025 * <p>This method is an explicit Runge-Kutta method, its Butcher-array 026 * is the following one : 027 * <pre> 028 * 0 | 0 0 0 0 029 * 1/3 | 1/3 0 0 0 030 * 2/3 |-1/3 1 0 0 031 * 1 | 1 -1 1 0 032 * |-------------------- 033 * | 1/8 3/8 3/8 1/8 034 * </pre> 035 * 036 * @see EulerIntegrator 037 * @see ClassicalRungeKuttaIntegrator 038 * @see GillIntegrator 039 * @see MidpointIntegrator 040 * @see LutherIntegrator 041 * @since 1.2 042 */ 043 044public class ThreeEighthesIntegrator extends RungeKuttaIntegrator { 045 046 /** Time steps Butcher array. */ 047 private static final double[] STATIC_C = { 048 1.0 / 3.0, 2.0 / 3.0, 1.0 049 }; 050 051 /** Internal weights Butcher array. */ 052 private static final double[][] STATIC_A = { 053 { 1.0 / 3.0 }, 054 { -1.0 / 3.0, 1.0 }, 055 { 1.0, -1.0, 1.0 } 056 }; 057 058 /** Propagation weights Butcher array. */ 059 private static final double[] STATIC_B = { 060 1.0 / 8.0, 3.0 / 8.0, 3.0 / 8.0, 1.0 / 8.0 061 }; 062 063 /** Simple constructor. 064 * Build a 3/8 integrator with the given step. 065 * @param step integration step 066 */ 067 public ThreeEighthesIntegrator(final double step) { 068 super("3/8", STATIC_C, STATIC_A, STATIC_B, new ThreeEighthesStepInterpolator(), step); 069 } 070}